Change volume on individual apps

I was wondering if someone knew a tool for changing volume on individual apps, or at least muting apps. When I am listening to music I hate websites etc that makes sounds, so I would like to only allow iTunes to play sounds.

Any help appreciated.

Thanks in advance.

"Gameplay Uber Alles. And if you can make it psychedelic too, great!" - Jeff Minter

Click to Flash is one of the most useful Mac apps *ever*. It also points out just how useless Flash really is. 99% of the boxes with "Flash" in them that I see now where Flash apps are blocked are adverts and in some sites I'm actually seeing Flash being used for non animating, non interactive graphics, ie where a png would be better.